Spectral index at 873–1226 µm (α_b6−b7). Left panel: color image of the spatially resolved distribution of α_b6−b7. Contours are the same as those in the right panel of Figure 1. The circles (with 30^◦ intervals in deprojected position angles) indicate the 50, 60, 70, and 80 AU deprojected radii. Right panel: values of α_b6−b7 at 50, 60, 70, and 80 AU deprojected radii as functions of the deprojected position angle, ϕ.